The number of echoes combined into a single image or image set in multiple echo imaging sequences or echo-train techniques such as rapid acquisition with relaxation enhancement (RARE), fast-spin echo (FSE), and turbo spin-echo (TSE). In RARE imaging, the ETL typically equals the acceleration factor.
As for tooth pain, it is caused by a reaction of the nerves inside a tooth's pulp chamber with the severity dependent upon the type and degree of the stimulus. What follows are some examples of symptoms you may be feeling and their possible causes.
There are many causes of tooth sensitivity, including: 1  Worn tooth enamel from using a hard toothbrush or brushing too aggressively. 2  Tooth erosion due to highly acidic foods and beverages. 3  Tooth erosion due to bulimia or gastroesophageal reflux disease (GERD)  Gum recession that leaves your root surface exposed.